1. Technical Field of the Invention
The invention relates to an optical reproducing method and an optical reproducing apparatus.
2. Related Art
In a holographic data storage, a signal light pattern representing digital data per one page in a brightness image is displayed on a spatial light modulator, a signal light modulated per pixel is generated, and the signal light is Fourier transformed by a lens and the transformed signal light is irradiated onto an optical recording medium together with a reference light. The Fourier transformed hologram of the data page is recorded in the optical recording medium due to interference between the signal light and the reference light. Plural pages of holograms may be recorded in a multiplex manner according to various multiplexing methods such as an angular multiplexing, in which an angle of incidence of the reference light is changed, for example.
In recent days, there has been proposed “coaxial recording method (collinear method)” as a recording and reproducing method of a holographic memory. In this collinear method, the signal light and the reference light are generated by modulating using the same spatial light modulator. The generated signal light and reference light are condensed by the same lens to have a common optic axis. The hologram is recorded in the optical recording medium due to interference between the signal light and the reference light. The signal light is reproduced from the recorded hologram by irradiating the reference light as a reading light.
In a case of executing a hologram reproducing method for obtaining a reproduced image by applying a direct-current component to a diffracted light, while using the collinear method mentioned above, a reference light and a direct-current component to be applied are generated using the same spatial light modulator at a time of reproducing. Accordingly, in order to apply the direct-current components in different phases for the positive image and the negative image, it is necessary to perform reproducing operation twice.